The Study Of Geochemistry Of Coals In The Southern Margin Of Ordos Basin

The coal quality and petrology,mineral composition and distribution characteristics,occurrence mode and enrichment mechanism of elements in coal of the southern margin of Ordos Basin were studied using the knowledge of coal petrology,mineralogy and geochemistry with the methods of proximate analysis,X fluorescence spectrometer(XRF),inductively coupled plasma mass spectrometry(ICP-MS),X-ray diffraction(XRD),scanning electron microscopy and energy dispersion spectrum(SEM-EDX),et al.The major achievements and understanding are as follows:The coal in Weibei C-P coalfield is mainly high rank bituminous coal with medium ash.The 11#coal of Taiyuan Formation has high organic sulfur(So,ad=3.85%),while the other main coal seams are low-sulfur coals.The maceral in the late Palaeozoic coal are mainly vitrinite,which indicates the coal seam was subjected to a strong gelation.The preservation of plant tissues was relatively poor.The Jurassic coals in the Binchang area are low rank bituminous coals with low ash and special low sulfur.The maceral in Jurassic coals in Binchang area are mainly inertinite.The coals in Yanan Formation of Binchang area were formed in a relatively dry and oxidized-weakly oxidized environment,the plant tissues of the coal-forming plants were well preserved.The minerals in coals in the study area are dominated by clay minerals,quartz,pyrite,cal cite,siderite,apatite,gypsum and anatase.The pyrite in the coal of Taiyuan Formation were found in the form of spheroidal,fine dispersion,cloddy,nodular,and epigenetic vein,indicating the pyrite were formed during several periods,which provided strong evidence of the influence of seawater to the formation of coal seam.The associated metal element Li in the coals of Weibei C-P coalfield is highly enriched(CC=11.79);Li,Th and U are mainly occurred in clay minerals.The environmentally sensitive elements Hg(2.51),Se(2.47),and Pb(2.29)are slightly enriched in the late Paleozoic coals;Hg,Se,As and Pb are mainly occurred in pyrite The associated metal element Cr,Co,Cu,Zn,Pb and Th in Jurassic coals of Binchang area are slightly higher than the average world coal.F in coals has both organic and inorganic affinity;Be is mainly occurred in clay minerals and organic matter.Different from previous studies of rare earth elements in the late Paleozoic coal of North China,the contents of ?REY in the Taiyuan Formation(130.9?g/g)are much higher than those of Shanxi Formation(87.1?g/g).The type of REY enrichment in coal of Weibei area is L-REY;the ?Eu in coal appears to negative anomaly,which shows strong inheritance of material sources;?Ce in coal appears to weak negative anomaly,indicating the sedimentary environment of peat swamp was between the reduction and weak oxidation.In the study area,the inorganic affinity of REY is much stronger and mineralogical modes of occurrence of REY are dominated by clay minerals and apatite,while pyrite has little contribution.The provenance of Weibei C-P coalfield and Huanglong J coalfield is mainly derived from the sedimentary rock and granite in the North Qinling oldland.The content and distribution characteristics of trace elements in coals of Weibei area are mainly controlled by the terrigenous parent rock and sedimentary environment,while the input of acidic volcanic ash and the leaching of groundwater also play important role in the enrichment of trace elements in coal.